Patent Application
20060293766
The present invention generally relates to oscillatory control technology and more particularly, relates to an oscillatory control system and method for compensating for time delays and for dampening unwanted oscillation signals in a control system.
In the case of motor torque being used to damp out mechanical oscillations, the phase relationship between the control action of an actuator, the motor torque, and the mechanical deflection or unwanted oscillatory signal that is being damped out is important for the damping action to be effective.
Motor control and active motor damping strategies are often used in automobiles and other vehicles powered by electric motors or vehicles having a hybrid ICE electric motor power configuration, typically called Hybrid Electric Vehicles (HEVs).
HEV configurations may include a series hybrid electric vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that work together in varying degrees to provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
For example in a driveline having a drive motor, such as a traction control motor in an HEV. The drive motor during normal drive and braking operations exerts a torque on the drivetrain to drive the wheels and unwanted oscillations in the driveline can occur due to motor inertia.
Control systems that use methods such as derivative control are often used in torque control strategies to provide a desired amount of torque generated by a motor to a mechanical system, such as a driveline in a vehicle having wheels driven by the motor.
Typically, as shown in prior art
Additionally, existing control systems often have time delays associated with sensing, computation, and actuation, however, time delays often reduce the effectiveness of the system by increasing the phase lag of the controlled output. There are techniques for compensating for time delays such as the use of derivative control, but these methods are sometimes either infeasible or insufficient.
It is common for vehicle traction motor controllers to include some sort of torque oscillation control feature in a motor torque control strategy.
Existing torque control methods may operate to eliminate vibrations in the driveline by controlling a flux producing current to the motor. Such a system is disclosed in U.S. Pat. No. 6,429,610B1 issued to Russell (RUSSELL). RUSSELL uses a flux producing current that is proportional to the speed of the motor to compensate for excessive motor vibration.
U.S. Pat. No. 6,002,232 issued to McConnell et. al. discloses various Robust Vibration Suppression methods and systems that use a control system to improve system performance in robustness, noise or speed as desired by a user. However, the McConnell reference does not compensate for phase errors or time delays between an unwanted oscillatory sign and an output control signal.
Many control systems, such as U.S. Pat. No. 5,304,907 issued to Abe et al. (ABE) provide a controller to maintain a required phase relationship between an actuator output, such as a servo motor system, and an unwanted oscillating signal. However, such systems, like the ABE invention require complex equipment and circuitry.
Therefore it is desirable to provide a simple control system that compensates for time delays in a controller using a modified input control signal to improve the effectiveness of the input control signal to reduce both time lag and phase errors and thus, efficiently control the oscillatory signal.
The present invention provides an oscillatory control system and method for compensating for time delays associated with oscillatory signals in a control system. Oscillations are defined herein as a cyclic signal.
Generally, the oscillatory control system provides:
In general, a general oscillatory control method for compensating for time delays in oscillatory signals detected in a control system is provided. Preferably, the present invention may dampen unwanted oscillatory signals, the general oscillatory control method has the steps of:
Additional steps are provided to the general method of the present invention in a first preferred embodiment. The first preferred embodiment additionally provides the steps of:
Alternatively, alternative additional steps are provided to the general method of the present invention in a second preferred embodiment. The second oscillatory control method for compensating for time delays in an oscillatory control system is provided, the second oscillatory control method has the steps of:
These and other objects, features and advantages of the present invention will become apparent from the following detailed description and the appended drawings in which:
The present invention provides an oscillatory control system and method for compensating for time delays and for dampening unwanted oscillation signals in a control system.
The present invention may be used to compensate for time delays and phase lags in an oscillatory control system. The present invention may be used in a system intended to eliminate unwanted oscillations in a system having a motor that generates torque as well as unwanted oscillations within a mechanical system. For example, the oscillatory control method of the present invention may be used in a system intended to actively damp unwanted driveline oscillations in any type of motor vehicle including HEVs. Additional applications for the present invention may also include, but not should not be limited to, suspension systems, electronic steering systems, and servo control mechanisms.
Referring now to the drawings, as shown in
As shown in prior art
The present invention operates to compensate for the time delay allowing the control system to effectively dampen the unwanted oscillation signal by providing an output signal TCout 32 that is an enhanced and modified TCin signal 28.
In general, the present invention provides for detection of an oscillatory signal, or detection of conditions that may cause an oscillatory signal to arise and provides a corresponding input control signal that has a value that ranges between at least one maximum peak and at least one minimum peak. The input control signal is oscillatory and related to a corresponding oscillatory signal.
An output signal that is substantially similar to the input control signal is provided to input into an actuator and thus, to compensate for time delays and phase lags in the input control signal.
In a preferred embodiment of the method of the present invention, the output signal is commanded to the value about which the oscillation of the input control signal is centered, the central value (CV), when the input control signal value drops below a delta amount of the at least one maximum peak value. Next, the output signal is set equal to the central value until the input control signal becomes less than the central value. Once the input control signal becomes less than the central value, the output signal is set equal to the input control signal.
Additionally, the output signal is commanded to the central value when the input control signal rises above a delta amount of the at least one minimum peak. Next, the output signal is set equal to the central value until the input control signal becomes greater than the central value. Once the input control signal becomes greater than the central value, the output signal is set equal to the input control signal.
If the input control signal has not dropped below a delta amount of the at least one maximum peak, then the output signal is set equal to the input control signal.
Alternatively, if the input control signal has not risen above a delta amount of the at least one minimum peak, then the output signal is set equal to the input control signal.
In an alternate preferred embodiment of the method of the present invention, the output signal is offset when the input control signal drops a delta amount below the at least one maximum peak until the input control signal becomes less than the central value of the oscillation and the slope of the input control signal becomes positive. Once the input control signal becomes less than the central value and the slope of the input control signal becomes positive, the output signal is set equal to the input control signal.
Alternatively, the output signal is offset when the input control signal rises by a delta amount above the at least one minimum peak until the input control signal becomes greater than the central value and the slope of the input control signal becomes negative. Once the input control signal becomes greater than the central value and the slope of the input control signal becomes negative, the output signal is set equal to the input control signal.
Preferably, the output signal is offset by an offset value large enough to drive the output signal past the central value of the oscillation and toward the opposite peak.
In one preferred embodiment, as shown in
As shown in
More particularly,
Initially, as shown in
More particularly, as shown in
Next, as shown in
If TCin is greater than the central value, then a maximum TCpeak value is determined (step 50). Step 50 has the substeps 52 and 54 as described below.
A determination is made whether TCin is greater than TCpeak (step 52).
When TCin is greater than the central value, if TCin is not greater than TCpeak, then it is determined if TCin is greater than TCpeak minus a delta amount (Δ) (delta amount shown in
If TCin is greater than TCpeak, then TCpeak is set equal to TCin (step 54), and then step 58 is performed.
After performing step 58, if the TCin is greater than TCpeak minus Δ, then an output signal TCout is set equal to TCin (step 60) and then steps 46, 48, 50, 58, and 60 or 64, are repeated if TCin is greater than the central value. However, if the TCin not greater than TCpeak minus Δ, then TCout is set equal to the central value (step 64) and steps 46, 48, 50, 58, and 60 are repeated if TCin is greater than the central value.
If TCin is not greater than the central value, then a minimum TCpeak value is determined (step 68). Step 68 has the substeps 70 and 72 as described below.
A determination is made whether TCin is less than TCpeak (step 70).
When TCin is less than the central value, if TCin is not less than TCpeak, then it is determined if TCin is less than TCpeak minus a delta amount (Δ) (delta amount shown in
If TCin is less than TCpeak, then TCpeak is set equal to TCin (step 72), and then step 76 is performed.
After performing step 76, if the TCin is less than TCpeak plus Δ, then an output signal TCout is set equal to TCin (step 78) and then steps 46, 48, 68, 76, and 78 or 82, are repeated. However, if the TCin is not less than TCpeak plus Δ, then TCout is set equal to the central value (step 82) and steps 46, 48, 68, 76, and 78 or 82 are repeated if TCin is less than the central value.
Referring now to
As shown in
Furthermore, as the command continues to move away from the peak value, the compensated command is correspondingly increased toward the opposite peak. This triggers the transition, at the maximum rate, from the positive to the negative peak, or vice versa, sooner than it would otherwise occur. The result is reduced controller delay and reduced phase error, thus making the control system more effective. This embodiment differs from the first embodiment by causing the control signal output or actuator command TCout to go from near one peak through the central value and toward the opposite peak sooner.
As defined in this embodiment, a torque_command_in is a torque command signal before the compensation method of the present invention is applied (see prior art
A torque_command_out signal or value is a torque command after the compensation method in accordance with the present embodiment is applied. The torque_command_out is assumed to be a signed variable.
A torque_command_fraction is a parameter that is a positive value between 0 and 1 (0<torque_command_fraction<1).
The torq_command_peak is an internal variable that is initialized to the central value.
A method 86 of the present invention operates to compensate for the time delay by providing a torq_commd_out signal that is a modified torq_commd_in signal. The torq_commd_out signal is similar to the torq_commd_in signal, however, the torq_commd_out signal is modified by an offset when the torq_commd_in drops below a threshold value representing a change in the TCin signal from the peak value, TCpeak toward the central value of the oscillation, wherein the peak torq_commd_in peak value (torq_commd_peak) is a sampled torq_commd_in value previously calculated at the highest or lowest value or strength value of the torq_commd_in signal.
Generally, the method 86 shown in
More particularly, as shown in
More particularly, as shown in
Next, as shown in
Next, as shown in
More particularly, as shown in
setting torq_commd_peak equal to torq_commd_in if a current torq_commd_in calculated value at a time Tn is greater than the value of torq_commd_peak (step 102); and
determining if a slope (torq_commd_slope) of the torq_commd_in is less than zero (thus indicating a decreasing or negative slope) or if an offset value, indicating a fractional value of the quantity torq_commd_peak minus the central value, is greater than zero (step 104).
As shown in
Step 110 has a substep 106 of setting an offset value equal to a torq_commd_fraction multiplied by the quantity torq_commd_peak minus the central value if the slope (torq_commd_slope) of the torq_commd_in is less than zero (thus indicating a decreasing or negative slope) or if the offset is greater than zero (step 104).
Step 110 is performed by determining if the offset is greater than zero and if either the torq_commd_in is greater than the quantity torq_commd_peak minus a selected amount, Δ, or the torq_commd_slope is greater than zero (step 111).
Next, a torq_commd_out, as shown in
However, a torq_commd_out is set equal to the torq_commd_in minus the offset if either the offset is not greater than zero or both the torq_commd_in is not greater than the quantity torq_commd_peak minus a selected amount, A, and the torq_commd_slope is not greater than zero(step 114).
After completing step 112 or step 114, steps 94 and 98 are repeated to determine a next torq_commd_in and to repeat either steps 108, 110, 112, and 114 if the torq_commd_in is greater than the central value or steps 124, 126, 128, and 130 if torq_commd_in is less than the central value using the iterative process of the present invention.
Alternatively, as shown in
More particularly, as shown in
As shown in
Step 126 has a substep 122 of setting an offset value equal to a torq_commd_fraction multiplied by the quantity torq_commd_peak minus the central value if a slope (torq_commd_slope) of the torq_commd_in is greater than zero (thus indicating an increasing or positive slope) or if the offset is less than zero (step 120).
Step 126 is further performed by determining if both the offset is less than zero and either the torq_commd_in is less than the quantity torq_commd_peak plus a selected amount, Δ, or if the torq_commd_slope is less than zero (step 127).
Next, a torq_commd_out is set equal to the torq_commd_in if the offset is less than zero and if either the torq_commd_in is less than the quantity torq_commd_peak plus a selected amount, Δ, or the torq_commd_slope is less than zero (step 128).
However, a torq_commd_out is set equal to the torq_commd_in minus the offset if either the offset is not less than zero or both the torq_commd_in is not less than the quantity torq_commd_peak plus a selected amount, Δ, and the torq_commd_slope is not less than zero(step 130).
After completing step 128 or step 130, steps 94 and 98 are repeated to determine a next torq_commd_in and to repeat either steps 108, 110, 112, and 114 if the torq_commd_in is greater than the central value or steps 124, 126, 128, and 130 if torq_commd_in is less than the central value using the iterative process of the present invention.
From the foregoing, it should be appreciated that several embodiments of a compensation system and method for oscillatory control have been provided.
While several preferred embodiments have been presented in the foregoing detailed description, it should be understood that a vast number of variations exist and the several preferred embodiments are merely examples, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the foregoing detailed description provides those of ordinary skill in the art with a convenient guide for implementing preferred embodiments of the invention and various changes can be made in the function and arrangements of the exemplary embodiment without departing from the spirit and scope of the appended claims.
